A monostable circuit of a voltage-to-frequency converter supplies feedback pulses to balance the input signal to a first integrator. These same pulses are supplied to a second integrator where they are compared with reference pulses from a crystal-controlled clock. Any drift in the pulse-width of the feedback pulses is corrected by a control signal applied to the monostable circuit by the second integrator to vary its quasi-stable period appropriately. Thus the precision of the converter is improved without disturbing its asynchronous properties.
An analog current-to-frequency converter which produces output pulses whose repetition rate depends on the current value. Included in the converter is an operational amplifier having an inverting input to which is applied a negative input voltage whose magnitude is proportional to the current value. The amplifier functions as an integrator which yields a positive output only when the voltage at its inverting input is negative. The integrator output is so coupled to the input of a one-shot as to cause the one-shot to generate an output pulse each time the integrator output crosses over from negative to positive. A NOR gate coupled to the one-shot acts to activate a switch only when the integrator output goes positive, the activated switch applying a positive reference voltage to the inverting input of the integrator through a balance resistor, thereby initiating a swing from negative to positive until a point is reached at which the integrator output goes from positive to negative. At this point the switch is deactivated to remove the positive reference voltage, the integrator output again going positive as a result of which the one-shot generates another pulse. Thus the integrator output in response to the applied negative input voltage oscillates from positive to negative to cause the one-shot controlled thereby to generate output pulses whose repetition rate is proportional to the value of the current being converted.
